I currently have a USDM 05 G35 Sedan RWD 5AT and looking to buy another transmission. I've found plenty of JDM transmissions for 03-05 but will they bolt right up or will I need other parts and sensors?

 

They're the same, there was a single MAJOR revision in the transmission which relocated the TCM into the transmission instead of being next to the ECM. You can tell them apart because the early model external TCM tranny had 3 bundles of wires with green harnesses coming out of it and the newer internal TCM ones have a single large grey connector at the grommet where the other wires came out of the tranny.

You can still swap the TCM and valve bodies between the two, so if you buy the wrong one you can take your existing TCM and wiring harness and swap it.